Khai triển: (a + b + c)^2 ; (a + b - c)^2
Khai triển: (a + b + c)2; (a + b – c)2.
• (a + b + c)2 = [(a + b) + c]2
= (a + b)2 + 2(a + b).c + c2
= a2 + 2ab + b2 + 2ac + 2bc + c2
= a2 + b2 + c2 + 2ab + 2ac + 2bc
• (a + b – c)2 = [(a + b) – c]2
= (a + b)2 – 2(a + b)c + c2
= a2 + b2 + 2ab – 2ac – 2bc + c2
= a2 + b2 + c2 + 2ab – 2ac – 2bc